As described herein, in certain aspects of the disclosure, hydrogen peroxide may be produced as a near-ideal gas phase, purified hydrogen peroxide gas (PHPG). In this form hydrogen peroxide behaves, in all respects, as a near-ideal gas and is not hydrated, or otherwise combined with water when produced.
The fundamental nature of a photocatalytic process is to create active intermediates in a chemical reaction by absorption of light. This occurs when a photon of the appropriate wavelength strikes the photocatalyst. The energy of the photon is imparted to a valence band electron, promoting the electron to the conduction band, thus leaving a “hole” in the valence band. In the absence of an adsorbed chemical species, the promoted electron will decay and recombine with the valence band hole. Recombination is prevented when the valence band hole captures an electron from an oxidizable species—preferentially molecular water—adsorbed to an active surface site on the photocatalyst. Concurrently, a reducible species adsorbed on the catalyst surface—preferentially molecular oxygen—may capture a conduction band electron.
Upon initiation of the photocatalytic process, or at the entrance point of a photocatalytic plasma reactor, the following reactions occur.
Oxidation2 photons+2H2O→2OH*+2H++2e−2OH*→H2O2 
ReductionO2±2H++2e→H2O2 
Once hydrogen peroxide has been produced, however, the photocatalyst preferentially reduces hydrogen peroxide (reduction potential 0.71 eV) instead of molecular oxygen (reduction potential −0.13 eV), and the reaction shifts to the following equilibrium which takes place within the majority of the plasma reactor volume.
Oxidation2 photons+2H2O→2OH*+2H++2e−2OH*→H2O2 
ReductionH2O2+2H++2e→2H2O
In the context of the present disclosure, near-ideal gas Purified Hydrogen Peroxide Gas (PHPG) may be produced using a photocatalytic process with a purpose-designed morphology that enables the removal of near-ideal gas phase hydrogen peroxide from the PHPG reactor before it is forced to undergo subsequent reduction by the photocatalyst. Denied ready availability of adsorbed hydrogen peroxide gas, the photocatalyst is then forced to preferentially reduce oxygen, rather than hydrogen peroxide. Hydrogen peroxide gas may then generally be produced simultaneously by both the oxidation of water and the reduction of dioxygen in the photocatalytic process. Without intending to be limited, in operation the amount of hydrogen peroxide produced may be doubled, then removed from the system before the vast majority of it can be reduced—thereby resulting in an output of near-ideal gas PHPG that is thousands of times greater than the incidental output of unpurified hydrogen peroxide from an equal number of active catalyst sites within a photocatalytic plasma reactor under the same conditions. This purpose-designed morphology also enables the production of near-ideal gas PHPG at absolute humidities well below those at which a photocatalytic plasma reactor can effectively operate. For example, near-ideal gas PHPG outputs greater than 5.0 ppm have been achieved at an absolute humidity of 2.5 milligrams per Liter. In the purpose-designed morphology the dominant reactions become:
Oxidation2 photons+2H2O→2OH*+2H++2e−2OH*→H2O2 
ReductionO2±2H++2e−→H2O2 
However, without being limited by theory, it should be noted that methods and devices of the present disclosure are not achieved as a result of the photocatalytic process, but by the effects of near-ideal gas PHPG once it is released into the environment.
Using morphology that permits immediate removal of hydrogen peroxide gas before it can be reduced, near-ideal gas PHPG may be generated in any suitable manner known in the art, including but not limited to, any suitable process known in the art that simultaneously oxidizes water in gas form and reduces oxygen gas, including gas phase photo-catalysis, e.g., using a metal catalyst such as titanium dioxide, zirconium oxide, titanium dioxide doped with cocatalysts (such as copper, rhodium, silver, platinum, gold, etc.), or other suitable metal oxide photocatalysts. Near-ideal gas PHPG may also be produced by electrolytic processes using anodes and cathodes made from any suitable metal, or constructed from metal oxide ceramics using morphology that permits immediate removal of hydrogen peroxide gas before it can be reduced. Alternatively, near-ideal gas PHPG may be produced by high frequency excitation of gaseous water and oxygen molecules on a suitable supporting substrate using morphology that permits immediate removal of hydrogen peroxide gas before it can be reduced.
As a near-ideal gas, hydrogen peroxide is not appreciably lighter than or heavier than air, having a molar mass of 34.0148 grams per mole. Near-ideal gas phase hydrogen peroxide diffuses through air as any other near-ideal gas would, and passes through air-permeable materials, unhindered by the surface tension of water as is seen in the behavior of micro-droplets comprising aqueous phase vapor forms of hydrogen peroxide often referred to as gaseous.
In this form, near-ideal gas phase hydrogen peroxide can penetrate to any space that can be reached by air itself. This includes all areas in which arachnids and insects are present in a room, such as crevices between materials, inside air-permeable cushions and in air-permeable bedding.
Continuously produced via a PHPG diffuser device, as discussed herein, an equilibrium concentration above 0.04 parts per million of near-ideal gas phase hydrogen peroxide may be achieved and maintained continuously in an environment. At equilibrium at one atmosphere pressure and 19.51 degrees Celsius, near-ideal gas phase hydrogen peroxide will be present in every cubic micron of air at an average amount of one molecule per cubic micron for each 0.04 parts per million of concentration. At one part per million, the average number of hydrogen peroxide molecules per cubic micron will be 25, and at 3.2 parts per million it will be 80.
Not to be limited by theory, near-ideal gas phase hydrogen peroxide will be “inhaled” or processed by arthropods including but not limited to arachnids and insects along with air, causing damage to sensitive tissues and either killing the arthropod or resulting in changes in behavior. In the case of arachnids, near-ideal gas phase hydrogen peroxide passes through tracheal tubes and body apertures to reach sensitive tissues and the book lungs of arachnids. The result of continuous exposure to near-ideal gas phase hydrogen peroxide at even low concentrations is damage to the tissues used in air exchange, and the death of the arachnid. Most arthropods, including insects do not have lungs, but survive solely by distributing oxygen through the body by means of a network of tracheal tubes. By this means near-ideal gas phase hydrogen peroxide reaches every portion of an arthropod's body and causes death to the arthropod, such as an insect. Not to be limited by theory the near-ideal gas phase hydrogen peroxide damages their air exchange tissues.
By contrast, humans and other vertebrates have respiratory mechanisms that protect them from equivalent concentrations of near-ideal gas phase hydrogen peroxide. Human lungs produce hydrogen peroxide at high rates and a cubic micron of human lung secretion contains an equilibrium concentration of between 600 molecules, and 60,000 molecules of hydrogen peroxide in aqueous phase, along with enzymes that consume hydrogen peroxide and regulate its concentration. Enzymes such as lactoperoxidase and catalase which perform this function are known to have enzymatic velocities of thousands of molecular reactions per second.
In one aspect of the present disclosure, a method of controlling an arthropods, such as insects or arachnids, in an environment is disclosed. In certain aspects, the arthropods are part of a population or a plurality of populations. In certain aspects, an arthropod, insect, or arachnid population is totally or partially killed. The method generally comprises (a) generating a near-ideal gas comprised of Purified Hydrogen Peroxide Gas (PHPG) that is substantially free of, e.g., hydration (i.e., non-hydrated, in the form of water in solution or water molecules bonded by covalence, van der Waals forces, or London forces), ozone, plasma species, and/or organic species; and (b) directing the gas comprised of PHPG into the environment such that the PHPG controls arthropod, insect, or arachnid populations in the environment.
As used herein, the term “Purified Hydrogen Peroxide Gas” or PHPG generally means a gas form of hydrogen peroxide that is substantially free of at least hydration (in the form of water in solution or water molecules bonded by covalence, van der Waals forces, or London forces) and substantially free of ozone.
In accordance with the present disclosure, the terms “substantial absence of ozone” “substantially free of ozone”, etc., generally mean amounts of ozone below about 0.015 ppm, down to levels below the LOD (level of detection) for ozone. Such levels are below the generally accepted limits for human health. In this regard, the Food and Drug Administration (FDA) requires ozone output of indoor medical devices to be no more than 0.05 ppm of ozone. The Occupational Safety and Health Administration (OSHA) requires that workers not be exposed to an average concentration of more than 0.10 ppm of ozone for 8 hours. The National Institute of Occupational Safety and Health (NIOSH) recommends an upper limit of 0.10 ppm of ozone, not to be exceeded at any time. Environmental Protection Agency's (EPA's) National Ambient Air Quality Standard for ozone is a maximum 8 hour average outdoor concentration of 0.08 ppm. The diffuser devices described herein have consistently demonstrated that they do not produce ozone at levels detectable by means of a Draeger Tube.
In certain aspects, the method comprises (a) exposing a metal, or metal oxide, catalyst to ultraviolet light in the presence of humid purified ambient air under conditions so as to form near-ideal gas Purified Hydrogen Peroxide Gas (PHPG) that is substantially free of at least one of hydration (in the form of water in solution or water molecules bonded by covalence, van der Waals forces, or London forces), ozone, plasma species, and organic species; and (b) directing the PHPG into the environment such that the PHPG controls arthropods in the environment.
In one aspect, the ultraviolet light produces at least one wavelength in a range above about 181 nm, above about 185 nm, above about 187 nm, between about 182 nm and about 254 nm, between about 187 nm and about 250 nm, between about 188 nm and about 249 nm, between about 255 nm and about 380 nm, etc. In certain aspects, wavelengths between about 255 nm and 380 nm may be preferred to improve yields of PHPG.
In certain aspects, the amount of PHPG may vary from about 0.005 ppm to about 5.0 ppm, more particularly, from about 0.02 ppm to about 1.5 ppm, in the environment. In certain aspects, the amount of PHPG may vary from about 0.5 ppm to about 1.5 ppm. PHPG levels of 1.5 ppm using a feed of untreated air containing absolute humidity as low as 3.5 mg/L can consistently be achieved. More particularly, PHPG levels from about 0.09 ppm to about 5.0 ppm using humid re-circulated air, can be produced in the environment to be treated. Also provided for an included are methods of treating arthropod population comprising providing PHPG gas at between 0.4 to 1.0 ppm. In another aspect, PHPG may be provided at between 0.5 to 1.5 ppm for the control of arthropods. In certain embodiments, the level of PHPG is maintained at 1.0 ppm or less.
In certain aspects of the present disclosure, the humidity of the ambient air is preferably above about 1% relative humidity (RH), above about 5% RH, above about 10% RH, etc. In certain aspects, the humidity of the ambient air may be between about 10% and about 99% RH. In one aspect, the method of the present disclosure includes regulating the humidity of the ambient air within the range of about 5% to about 99% RH, or about 10 to about 99% RH.
A suitable diffuser device may be used to generate the near-ideal gas PHPG, such as those disclosed in WO/2009/021108 or WO/2010/093796, the contents of which are herein incorporated by reference in their entireties. The diffuser design may optimize near-ideal gas PHPG production by spreading the air permeable photocatalytic PHPG reactor surface thinly over a large area that is perpendicular to air flow (e.g., in certain aspects, over a sail-like area), rather than by compacting it into a volume-optimizing morphology designed to maximize residence time within the plasma reactor.
For example, by configuring the PHPG reactor morphology as a thin, sail-like air-permeable structure, just inside the diffuser's interior shell, the exit path length for hydrogen peroxide molecules produced on the catalyst becomes diminishingly short, and their residence time within the PHPG reactor structure is reduced to a fraction of a second, preventing the vast majority of hydrogen peroxide molecules from being subsequently adsorbed onto the catalyst and reduced back into water. Also, by placing the catalyst substrate just inside the interior surface of the diffuser shell, not only is PHPG reactor surface area maximized, but the near-ideal gas PHPG produced also passes out of the diffuser almost immediately and thus avoids photolysis from prolonged exposure to the UV light source. By means of this morphology, near-ideal gas PHPG output concentrations as high as 0.40 ppm may be achieved.
Generally, the present disclosure has been described in specific aspects with some degree of particularity, it is to be understood that this description has been given only by way of example and that numerous changes in the details of construction, fabrication and use, including the combination and arrangement of parts, may be made without departing from the spirit and scope of the present disclosure as shown in the following example aspects.
In previous disclosures, obstacles in the field to produce highly concentrated non-hydrated Purified Hydrogen Peroxide Gas, are overcome and the production of PHPG has many applications in domestic, industrial, and agricultural arenas. While conducting studies on the performance and PHPG output of a PHPG producing apparatus and its activity on molds, bacteria and viruses, the surprising and unexpected observation that near-ideal gas phase hydrogen peroxide can be used to kill, partially kill, or modify the behavior of most species of arthropods including insects and arachnids, among others. Without being limited by a particular theory, the surprising effects of PHPG gas on the behavior of many species of insects and arachnids may be due at least in part because many species of arthropods appear to have limited or no natural protection against hydrogen peroxide gas.
Surprisingly, the inventors also discovered that non-hydrated hydrogen peroxide gas acts as a repellant against arthropods including arachnids, flying insects, and crawling insects, causing them to flee an area protected by the hydrogen peroxide gas and preventing them from entering the area. Further, the inventors found that hydrogen peroxide gas causes many species of arthropods that are unable to flee a PHPG enriched area to become inactive and die over a period of time ranging from hours to days. The inventors also observed that hydrogen peroxide gas can interrupt the life cycle of many species of arthropods, even causing pupae, larvae, and nits to die. Based on these findings, the application of PHPG gas to arthropod control has a wide range of beneficial uses in the domestic, industrial and agricultural industries.
In addition to the broad effectiveness of PHPG for the control of arthropods, PHPG, used at concentrations below a few parts per million, acts as a “green” pesticide which breaks down into water and oxygen in the environment, leaving no toxic residue, and is not harmful to humans, pets, or plants.